66 
NAUTILOIDEA. 
transverse section is nearly circular in the young, hut becomes suh- 
quadrate with rounded angles in the adult, through the flattening 
of the convex side. The septa are moderately distant from each 
other (2 lines apart where the ventro-dorsal diameter is 5 lines) ; 
the sutures form a shallow sinus upon the sides, bend forwards at 
the lateral angles, and make another slight sinus in crossing the 
periphery. There are about twenty-two septa in a complete whorl. 
The body-chamber is large, and occupies at least half the last whorl. 
The siphuncle is small and is situated between the centre and the 
convex border. The test is beautifully ornamented with longitu- 
dinal, parallel ridges, which are crossed by strong sigmoid raised 
lines, which form a series of nodes or small tubercles at their inter- 
section with the ridges. The latter become obsolete upon the last 
whorl, and only the transverse ornaments are present. 
Remarhs. This species is easily recognized by the ornamentation 
and septation, which are well displayed in the specimens in the 
British Museum which I have referred to it. 
Horizon. Carboniferous Limestone. 
Locality. Kildare. 
Well represented in the Collection. 
Gyroceras tessellatum, de Koninck. 
1844. CyHoceras tessellatum, de Koniuck, Descr. des Aiilm. Fossiles du 
Terr. Carb. de la Belgique, p. 528, pi. xlviii. ff. 5a,b. 
1849. Aploceras tessellatum^ d’Orbigny, Prodr. de Pal»5ont. Stratigr. 
vol. i. p. 112. 
1852. Cyrtoceras tessellatum, Giebel, Fauna der Vorwelt, Band iii. 
Abth. i. p. 207. 
1876. Cyrtoceras tessellatum, F. Roemer, Lethsea Palseozoica, pi. xlvi. 
f. 2. 
1880. Gyroceras tessellatum, de Koninck, Faune du Calc. Carb. de la 
Belgique, pt. ii. (Annales du Mus. Roy. d’Hist. Nat. de Belgique, 
tom. V.) p. 13, pi. xxxiii. if. 6, 6 a. 
Sp. Char. Shell composed of one and a half to two whorls, very 
distant from each other ; the initial point obtuse. The transverse 
section is broadly subtri angular, except in the apical portion, where 
it is circular. The first whorl is slightly inflated at regular inter- 
vals. -The septa are numerous and closely approximate ; in a 
fragment which has a transverse diameter of about 1 inch their 
distance is only about 1 line ; they are regularly concave, shallow, 
and the sutures are straiglit. The siphuncle is small and is situated 
between the centre and the convex border. The surface of the test 
is ornamented with twenty-three longitudinal ridges, of which about 
